1. Field of the Invention
The present invention relates generally to steerable catheters, and more particularly to steerable ultrasound imaging catheters that can be maneuvered intravascularly throughout the cardiovascular system.
2. Description of the Related Art
Catheters for insertion and deployment within blood vessels and cardiac chambers are well-known in the art.
Endocardial catheter recording, mapping, and imaging probes have clinical roles in diagnosis and treatment of cardiovascular ailments including direct ablation, surgical, and drug therapies, in the treatment of supra-ventricular tachycardia, ventricular tachycardia, atrial flutter, atrial fibrillation and other arrhythmias. The addition of ultrasound imaging catheters to the ensemble of electrophysiology catheters has greatly improved the physician's ability to visualize endocardial structures, thus improving diagnosis and targeted ablation.
The success and advancement of current therapies will benefit from the development and use of more precise catheter positioning and localization techniques within a patient's body that will allow accurate anatomical determination of abnormal conductive pathways and other arrhythmogenic sites.
Improvements are needed in catheter steering systems in order to permit ultrasound imaging probes to reach specific targets and view regions of interests, such as within a patient's heart. Also, improved flexibility will permit the attending physician to more accurately maneuver and direct the ultrasound imaging catheter tip. Placement of prior art catheters within the heart has been generally restricted to areas which can be repeatedly accessed by the electrophysiologist. These areas include the (high right atrium) HRA, the (right ventricular apex) RVA, the (right ventricular outflow tract) RVOT, the coronary sinus, the atrial ventricular node (AV node) and near the HIS bundle. To obtain meaningful information about additional placement sites, the number of electrograms recorded over a given area may be increased, and the precise position of the electrode array of the distal tip portion of the catheter may be varied. Some of these additional sites include atrial sites above the tricuspid and mitral valves, ventricular sites circumferential to the mitral and tricuspid valve leaflets, distal areas of the coronary sinus and great cardiac vein, the AV nodal area and the left ventricle, in addition to other sites as would be readily apparent to one of ordinary skill in the art after reading this disclosure.
One area of advancement in improving catheter positioning techniques and accessing additional recording sites within a patient's heart is the use of steerable catheters. One type of prior art steerable catheter permits maneuvering the catheter to specific, otherwise inaccessible sites by being shaped specifically to access the particular site. Although perhaps useful for some less inaccessible sites, the use of this type of catheter is limited, not very practical, and not helpful in reaching sites requiring active articulation during placement.
Other prior art steerable catheters attempt to improve placement maneuverability by having bendable tips. These catheters include a relatively soft and flexible distal tip portion of a certain length attached to a proximal shaft made from a relatively stiffer material. Generally, the tip may be selectively deflected but only in a prescribed arc defining a plane. The tip of the catheter bends in one planar direction, with the bend having a fixed, predetermined radius of curvature, typically around four inches. A steering cable attached to the distal tip portion at or near the tip and running down the interior of the catheter is pulled proximally while the catheter shaft is restrained, thus causing the tip to deflect. Alternatively, the steering cable is restrained while the shaft portion is advanced distally, producing the same effect.
A disadvantage of the above-described preformed and deflecting tip type catheters is that the tip of the catheter in each case may be deflected or steered only in a prescribed configuration in only a single plane which cannot be altered during or after its placement. That is, the steerable tip has a single radius of curvature which is fixed, thus restricting the accessibility of the distal tip to certain anatomical sites, while other sites may not be accessible at all. Further, in order to direct the catheter tip into a passage at an angle to the deflection plane, the catheter must be straightened, rotated to align with the passage and then deflected. In some passages this may not be possible. Also, in the case of ultrasound imaging catheters, rotating the catheter may direct the imaging plane away from areas of interest.
As a result of the above described disadvantages of prior art steerable catheters, the electrophysiologist must obtain and maintain not one but a set of similar steerable electrode catheters for use during any single clinical evaluation of a patient. For example, the user will have on hand a catheter having a steerable tip having a small radius of curvature; another with a medium radius of curvature and a third with a relatively large radius of curvature. While this availability of differently radiused tips is beneficial, it is often not known by the electrophysiologist which size will be required prior to a diagnostic or therapeutic intracardiac procedure. Moreover, similar tip placements may require different radiused tips from one individual to another, even those of the same general body size and mass. When it is discovered by the electrophysiologist that a catheter then placed in a patient has an incorrectly radiused tip for the required procedure, the catheter must be completely withdrawn from the patient (through whichever one of the femoral, subclavian, jugular or brachial approaches was used), and a new properly radiused electrode catheter tip must be reintroduced into the heart. This substitution may take up to two hours or more to complete, including the time required to precisely reposition the electrode tip.
Moreover, the initially selected, but improperly sized catheter must generally be discarded, never having been actually used for its intended purpose, as such devices are intended as “single use only” devices for a variety of safety reasons. Steerable catheters are relatively expensive devices, and this waste of an otherwise good device is especially troublesome.
In response to these problems, steerable catheters have been developed which have an adjustable radius of curvature. These catheters require a radius control mechanism in addition to the steering control mechanism, which imposes additional level of complexity to their manufacture and use.
Other disadvantages are related to the limitations inherent in current pull cable steering systems. Such steering systems typically include a flat stainless steel shim or similar spring-like element in the area where the catheter tip is to be bent. One or more pull cables are secured to the shim or portion of the catheter adjacent the distal end of the shim and extend the length of the catheter to be manipulated by the physician in order to steer the catheter. These steering systems require additional locking for the bend or curve to be fixed for any period of time. Deflectable catheter tips of the type just described are generally resiliently biased due to the springs, which cause the catheter tips to return to a straight configuration when not acted upon by the pull cable mechanisms for causing tip deflection. Another drawback with such catheters, as a result of this resiliency, is the undesired tendency of the tip to return to an undeflected position, or to merely change the amount of deflection, during the course of the electrophysiological procedure. Locking mechanisms have been employed to secure the deflection, but this requires an additional step for the physician using the catheter. Such excessive maneuvering and the additional step of locking the catheter exteriorly of the patient is difficult, frustrating, time consuming and inefficient to the physician performing a delicate procedure, and is thus inherently more risky for the patient undergoing that procedure.
Another disadvantage to the current pull cable systems becomes even more evident when applied to ultrasound catheters, particularly those that are also used for electrophysiology applications. Most ultrasound catheters have a large number of ultrasound elements that form the transducer, and each requires a separate coaxial cable running through the length of the catheter body. This is in addition to the insulated electrical signal wires that run through the catheter bodies. All of these wires and cables leave little room for a spring shim or the like.
Another disadvantage in current imaging catheters is the cross-sectional diameter required to accommodate the steering cables and electrical wiring for imaging components. For example, a transducer with just sixty-four elements requires at least sixty-four cables running through the catheter, in addition to the steering cables. The number of cables increases with the number of transducer elements. For that reason, imaging catheters typically are no smaller than 10 French in diameter. Catheters with diameters of less than 10 French could be useful to navigate through small vessels in the body and to reduce potential injury to patients.
Therefore, a need exists for a steerable ultrasound catheter that is easier to construct, has a flexible and versatile distal end, which does not include metallic spring elements that may interfere with imaging, and which has a reduced cross-section. Other problems with the prior art not described above can also be overcome using the teachings of the present invention, as would be readily apparent to one of ordinary skill in the art after reading this disclosure.